1. Field of the Invention
The present invention relates to a hydraulic cylinder cushion device, and more particularly to a hydraulic cylinder cushion device that improves the cushion performance at a stroke end by a check ring.
2. Description of the Prior Art
FIGS. 1A to 1C are views illustrating an example of a hydraulic pneumatic cylinder in the related art. As shown in FIG. 1A, a cylinder briefly includes a tube 10 which serves as a pressure vessel and guides a rectilinear movement of a piston, a rod 20 which is a long circular bar shaped shaft portion that performs a rectilinear reciprocating movement; a head cover 30 having a packing mounted thereon to prevent outer leakage of hydraulic fluid in the tube; a piston which maintains hydraulic power in a large chamber and a small chamber provided in the tube; and a cushion ring 50 which absorbs mechanical impact at a stroke end.
FIG. 1B is a view exemplifying a state where a cushion ring 5 rushes into head cover 30, and FIG. 1C is a view exemplifying a time point where an initial operation starts on the opposite side after the entrance of the cushion ring is completed.
In the case of a cylinder with built-in cushion, as shown in FIGS. 1A to 1C, a cushion system is constructed to reduce the mechanical impact in a stroke end, and most approaching schemes are to construct a structure that reduces impact force through reduction of the speed of a piston 40. The speed of the piston 40 is reduced by gradually throttling a flow path through adjustment of an open area on an outlet flow path using a ring type or plunger type cushion system.
As illustrated in FIG. 1C, at the time point where the cushion tool's rushing into the stroke end is almost completed, a gap is kept in a minimum state for sufficient cushion, and the mutual contact surfaces of an end portion and an outer peripheral portion are in mutually strong surface contact with each other.
If the cushion gets out of the stroke end, an additional frictional force is formed, and a cross-sectional area for actually transferring the cylinder rod, although the hydraulic fluid has been transferred from the pump to the flow path, is formed only by the ring-shaped projection area of the cushion ring, which is too narrow. Accordingly, a time delay occurs until the pressure is accumulated and a sufficient force is formed.
According to some cylinders in the market, as shown in FIG. 2, a cushion chamber is inserted into the lower end of the cushion ring to lead the check function. In this case, however, since a groove process is performed with respect to one end of the rod, which copes with a relatively great force and is exposed at all times, there is possibility of damage due to the stress concentration.
From the viewpoint of the hydraulic system, as shown in FIG. 3, when the cylinder is initially operated at the stroke end, the operation of the discharge side of the pump is delayed due to the insufficiency of a pressed area in the cylinder, and thus the pressure is increased. Sometimes, the increased pressure reaches the relief pressure, and this cause unnecessary energy consumption. From the viewpoint of the cylinder operation, an instantaneous initial abrupt operation or the like occurs after the operation delay, and this causes a deathblow to the performance of the cylinder in the case where an elaborate work is required.
In addition, the above-described phenomenon aggravates fuel economy of the equipment due to the unnecessary energy consumption, and in order to give smooth initial operability, the phenomenon causes a system overdesign element such as an increase of pump capacity or the like to increase the cost.